CONTENTS ix 
CHAPTER XV 
Fina Remarks 
Sage ao PAGE 
Problems requiring investigation— 
Giant nerve-cells and giant nerve-fibres; their comparison in fishes and 
arthropods; blood- and lymph-corpuscles; nature of the skin; origin of 
system of unstriped muscles; origin of the sympathetic nervous system ; 
biological test of relationship. , 
Criticisms of Balanoglossus theory—Theory of parallel development—Importance 
of the theory advocated in this book for all problems of Evolution . . 488 
BIBLIOGRAPHY AND INDEX oF AUTHORS . ¥ i ‘ . ‘ . . 501 
GENERAL INDEX . ‘i ‘ 5 ‘ 5 : . ' : : , . 617 
